Process for liquefying and rectifying air



March 1933- M. HAZARD-FLAMAND PROCESS FOR LIQUEFYING AND RECTIFYING AIR Filea- Oct. 9, 1929 2 Sheets-Sheet l Fig.1

March 14, 1933. V M. HAZARD-FLAMAND 1,901,339

PROCESS FOR LIQUEFYING" AND RECTIFYING AIR Filed Oct. 9, 1929 2 Sheets-Sheet 2 Fig.2

Patented Mar. 14, 1933 PATENT OFFICE MAURICE HAZARD-FLAMAND, OF DOUAI, FRAIFCE PROCESS FOR LIQUEFYJING AND RECTIFYING AIR Application filed October 9, 1929, Serial No. 398,459, and in France October 18, 1928.

This invention relates to the liquefaction of air.

It is not new to cause air to be liquefied to be compressed at a pressure of 200 atm. and then to divide this air into two streams, one of which is expanded in the performance of work and the other by a throttle. It is also known to cool the air to be liquefied by means of a refrigerator.

19 It has been also proposed heretofore to divide the air into two streams, and to cool one of these streams by means of an additional refrigerator, the said stream being, however. compressed at a pressure lower than thatof the other stream.

According to the present invention, the cooling of the air compressed at 200 atm., which air is divided into two streams, is carried out by means of an additional refrigerator with liquefied gas, which is located in the circuit after the exchanger, but before the division into two streams of the air under pressure. all the mass of which is thus submitted to said cooling under the pressure of 200 atm.

The arrangement of -the refrigerator between the exchanger and the point of the circuit where the division of the air takes place has the following advantages: at the exhaust of the exchanger, the temperature of all the mass of air under pressure is reduced from 20 to approximately 10 In known processes using an exchanger, the temperature of the air at the admission thereof into the expander is reduced to approximately -100, which is disadvantageous; on the contrary, in the present invention, all the mass of compressed air, after its passage through the refrigerator, is cooled only to approximately the temperature of admission of the air into the expander thus being raised from 100 to -50 without the necessity, as is the case for known processes, of removing the exchanger (which re- 5 moval would cause a loss of cold at the exhaustof the counter current). This raise determines an increase in the output of the outer expansion and said increase, added to the almost cost free auxiliary cold supplied by the refrigerator (about 15 frigorie's per kilog. of compressed air), approximately doubles the production of liquid air per horse-power of compression.

The cost free auxiliary cold, which can be caused to be absorbed by the compressed air at the exhaust of an exchanger, is equal to the excess of its calorific power between about 20 and 50 over the amount of cold supplied by the counter current to thesame. But this amount is so much weaker that the o specific heat and the weight of the counter current are less. It results therefrom that it is necessary to send into the expander only a counter-current which is entirely expanded. The raise of the pressure of the com- 55 pressed air to 200 results in an increase in the specific heat and the calorific capacity of the mass of this air. Besides, the increase in the liquefaction owing to this high pressure reduces the importance of the countercurrent and, consequently, the amount of cold which is brought back into the system by the counter-current.

The process in accordance with the present invention'is carried out in the manner Y5 particularly described hereinafter, reference being had to the accompanying drawings, of which:

Fig. 1 is adiagrammatic view of apparatus used for effecting the liquefaction;

Fig. 2 illustrates diagrammatically how the liquefaction apparatus is combined with the rectification apparatus.

The air used for liquefaction is compressed at high'pres'sure, for example, 200 atmos- 85 pheres, by a compressor 1' and cooled in a water cooler 2. The air is then purified according to current practice and passed to an exchanger 3.

From exchanger 3 the air is conveyed to a a0 refrigerator 4 utilizing liquefied gas, for example, ammonia. After leaving refrigerator 4. the compressed and cooled air is divided into two parts. One part is led into a piston engine 9, in which it expands up to atmos- 9 pheric pressure. The other part, under a pressure of 200 atm., passes through a liquefying exchanger 5 and upon leaving the same is expanded to atmospheric pressure in an expansion vessel 6 through a tap, or 1 0 cock, 11. That portion of the expanded air which remains in a gaseous state is returned as a counter current to the exchangers, in conjunction with the exhaust of the expander 9 which may join the same either at the bottom of the liquefier 5, as shown, or in the expanding vessel 6. A cock 7 permits the liquefied air to be drawn ofil The liquefaction in the expander 9 is a very intensive one and couldv interfere with the operation thereof if suitable counter-acting provisions were not made, such as a tapping ofi device at the end of the piston stroke or a compounding with tapping off in the receiver. It may be desirable in some cases, even with a decrease in cooling action, to avoid complications in effecting reduction in condensation in expander 9. This result may be attained for example by lowering the pressure at which air is admitted to the expander by means of a cook or tap, 8, or by raising the temperature of admission of the air to motor 9, either at point 13 or partly at point 13 and partly at point 12.

In virtue of its arrangements and of its powerful output, the apparatus wh1ch has just been described is particularly well adapted to be coupled with one of the well known double column rectifiers.

It is well known that a prominent feature of this known rectifying apparatus consists in supplying to the lower column an excess of liquid nitrogen capable of rectifying in the upper column, at atmospheric pressure,

- a supplement ofair exceeding about 30% of the quantity supplied to the lower column. Now this quantity is usually about 30% greater than the exhaust of the expander of the liquefying machine associated with the column when the said machine is working at the rate of its maximum output.

It will therefore be possible, just as in other processes, to direct the exhaust of the condenser 5 into the lower column 17, either 7 directly or through a concentrating coil 18,

while, after complete expansion, the whole of the exhaust of the expander 9 will be directed upon the plate in the upper column 19. The excess of air to be rectified will be supplied to the rectifier by two compressors or a combined compressor 21 which will supply this partly compressed air into the lower column 17, and eventually partly at atmospheric pressure into the upper column 19. The counter-current of the liquefying apparatus will be secured by part of the nitrogen leaving the upper column 19.

What I claim is:

1'. A process for liquefying air which comprises passing the air under high pressure through an exchanger and then through a refrigerator, dividing the air after it has passed through the refri erator into two streams, expanding one 0 said streams in a low pressure liquefying chamber, expanding the other of said streams in a work performing device operable by the expansion, returning the unliquefied air under low pressure from the liquefying chamber in heat exchange relationship to the air flowing to the liquefying chamber, and also returning the expanded, low pressure air from the work performing device in heat exchange relationship to the air flowing to the liquefying chamber.

2. A process for liquefying air as set forth in claim 1 in which the return of the low pressure air from the liquefying chamber and the work performing device is directed in heat exchange relationship to the air flowing to the liquefying chamber both before and after the air flowing to the liquefying chamber passes through the refrigerator.

3. A process as set forth in claim 1 in which the low pressure air after being returned in heat exchange relationship to the air flowing to the liquefying chamber is directed into apparatus for separating the air into its constituents oxygen and nitrogen.

In testimony whereof I hereunto aflix my signature.

MAURICE HAZARD-FLAMAND. 

